LogScanner LRgon

The LogScanner™ project has just discovered a very important item which is called the LRgon™ (the left-right polygon).

What is a LRgon™?

The LRgon helps you find out whether you should have gone right or left. It is sort of like the GeoGons except that LogScanner calculates the location of two rectangles arranged so that 50% of each leg is in each rectangle. In the image, the red rectangle covers 50% of your passage to the left of the “mean rhumbline”, and the green rectangle covers the other 50% to the right.

LogScanner then compares the wind and current on one side vs. the other, the idea being to report which side provided better performance.

The image shows a windward leg where the boat went left. LogScanner reports that the right side wind was 9° clockwise and 1.5 knots slower than the left side. The true wind speed for the leg was 16 knots, so this difference would probably not make much difference.

Current has a very important effect on performance. Note the blue arrow where the boat is. It is ½ a knot downwind, which is equivalent to 80 seconds/mile loss. This makes current a very important thing to monitor. The current difference on the right side is ¼ knot less than the left side. Because the leg is 1.8 miles long, if the boat had gone right instead of left, they would have gotten to the mark 1.5 minutes faster!